Implement OpenAPIVerifier

[abdelfetah18]

This implementation of OpenAPIVerifier is fairly basic and supports three modes: Exact, AtLeast, and AtMost.

The verify method returns a list of issues. If the list is empty, it indicates a valid verification.

/claim #3645

[adamw]

Thanks! Can we move the functionality to a new module? We can't (shouldn't) add a circe dependency to the main openapi docs one.

Also, can you add a mention of the feature to the docs? I think a new section in https://tapir.softwaremill.com/en/latest/testing.html#endpoints-verification would be best

[adamw]

Thanks!